Gray and malleable cast iron typically contain between about 2 to about 5 wt % carbon as graphite. In fact, gray cast iron is so-called because when it is fractured the exposed interior surface is gray in color due to the graphite.
In machining metal parts a lubricating composition normally is used to serve not only as a lubricant but also as a coolant and to promote tool cleanliness. Conventional water mix lubricating compositions used in metal cooling consist of a base oil such as a petroleum basestock, a surfactant system, a corrosion inhibition system and a biocidal system. In use, the lubricating composition is mixed with water in the range of about 2 vol % to about 20 vol % oil to form an oil-in-water emulsion.
Experience has shown that in machining cast iron, such as gray cast iron, small particles of graphite are released into the emulsion and result in the formation of a black paste in the oil phase which not only is difficult to clean up but tends to foul the machine tool. This causes long machine tool downtime for tool changes and maintenance. Thus, there is a need for an emulsifiable lubricating composition which tends to reduce, if not prevent, graphite paste formation when the composition is used in machining graphite containing metals such as of cast iron.